rain through blocks from previous versions

It rains through certain blocks within my world. Some places all the way down to y=11. This affects both blocks placed by me and naturally generated ones, but not blocks I've placed recently, I believe past update 20w18a. These blocks appear not to be taken into account somewhere, they don't appear on maps either. I have updated the world through all of the snapshot versions, except version 20w13a and 20w20a. I started from version 20w12a onwards. The world was initially generated in version 1.14.4.